


Date derivative

by seoulfulnights



Category: Monsta X (Band)
Genre: Alternate Universe - High School, Crushes, Fluff and Humor, Light-Hearted, M/M, Mathematics, Romantic Comedy, but kihyun actually solves everything, hyungwon and minhyuk are pretty boys who don't math, so minhyuk tutors hyungwon duh
Language: English
Status: Completed
Published: 2019-04-06
Updated: 2019-04-06
Packaged: 2020-01-05 11:14:18
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,640
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18364877
Author URL: https://archiveofourown.org/users/seoulfulnights/pseuds/seoulfulnights
Summary: Scheming, Minhyuk likes to think, comes naturally to him as a proud Scorpio and Slytherin. The plan he comes up with is simple and consists of only three steps. Step one, become Hyungwon’s maths tutor. Step two, make Hyungwon fall in love with him. You might ask yourself what about step three, but if it wasn’t clear enough by now, maths really is not his best angle (but puns are, get it?).





	Date derivative

**Author's Note:**

  * For [jeolmeoniji](https://archiveofourown.org/users/jeolmeoniji/gifts).



> this story is for my dear friend @jeolmeoniji! thank you for being there for me in my hardest times and always believing in me. thank you for giving me this story to write and i hope i did your prompt justice
> 
> based on her post found [ here ](https://twitter.com/jeolmeoniji/status/1011682641014394880)

Most people at school knew Lee Minhyuk for his loud yet charismatic jokes and for always getting away with whatever folly crossed his mind. Despite talking over the teacher at all times, the boy managed to deliver a witty comeback whenever some aggravated professor would call him to the blackboard. Adding to his good looks, the boy was an overall sweet talker who could easily collect the souls of his fellow classmates just for fun. It was so easy for him to get whatever he wanted just because people would be so overly eager to spend time with _the_ Lee Minhyuk of Starship Academy.

Yet among his fellow peers in the same year, there was one boy ahead of him in the school hierarchy, a boy who nobody could ever dethrone. Chae Hyungwon. Rumored that he shot commercials in Japan for cars and that his lips are insured for over one million won, Chae Hyungwon could step on anyone and they’d say thank you. Minhyuk would be annoyed at how his own friend Im Changkyun would chant ‘the prince! the prince!’ whenever Hyungwon entered the cafeteria, but he understands the sentiment wholeheartedly. He’s just as smitten with Chae Hyungwon as any other rational guy at Starship Academy – perhaps not as intensely as his senior, Shin Hoseok, who never misses a day to leave a ‘secret’ admirer note in Hyungwon’s locker and a red rose on his desk, but _still_.

For somebody as popular as Chae Hyungwon, somebody who appeared to be the epitome of ethereal beauty and perfection, the boy had but one flaw. He was failing maths. Minhyuk could wholeheartedly understand the sentiment as he too barely managed to pass last term’s finals even with some tutoring from his best friend Yoo Kihyun, national champion representing South Korea in the International Mathematical Olympiad. Or for short, the biggest geek Minhyuk ever met and who will probably end up working for NASA or whatever geniuses like him do. But this ain’t about Kihyun. This is about himself and, well, prince charming Chae Hyungwon. “And about stealing his heart,” Minhyuk claims, grabbing the list of students in search for math mentors off the school’s board, only minutes after Hyungwon signed his name down.

Scheming, Minhyuk likes to think, comes naturally to him as a proud Scorpio and Slytherin. The plan he comes up with is simple and consists of only three steps. Step one, become Hyungwon’s maths tutor, already half-accomplished by stealing anyone else’s chance to offer themselves for the job. Step two, make Hyungwon fall in love with him, which should be no big complication given his charming personality. You might ask yourself what about step three, but if it wasn’t clear enough by now, maths _really_ is not his best angle (but puns are, get it?). Therefore, Minhyuk puts all his efforts in looking his very best next Thursday after class for their library date and doesn’t even bother to bring his own textbook or the pages of formulas Kihyun so neatly wrote for him.

With his uniform ironed, his tie perfectly knotted around his collar, and his best sneakers on his feet, Minhyuk enters full of confidence the quietest place in the whole school, which he successfully avoided for the past three years he attended Starship Academy. The librarian gives him a suspicious look from behind her glasses but Minhyuk pays her no mind and sets on a quest to find Hyungwon. Easy task – nobody else could be caught sleeping over a desk and yet looking as graciously like the popular boy. “Hello, Chae-ssi!” Minhyuk grins, a whole sun radiating from his smile and waking the other up. The librarian’s warning shushing would rather argue it’s actually his loud voice that did the job.

“Ready to be emerged in the fascinating world of mathematics?” he asks quite dramatically while pulling a chair for himself next to the other. So close to Hyungwon, he can appreciate the boy’s beauty much better, he can confirm all the rave about his flawless appearance, the allure of his pouty lips, the shine of his silky black hair. This tutoring should be ticked as some museum tour because Minhyuk’s sure he is admiring a masterpiece, a fine work of art. “Are you one of those drama kids?” Hyungwon mumbles, idly sorting out his notes and pulling a fresh sheet of paper to write on after finding in his textbook the chapter he’s having issues with. Drama? Minhyuk certainly knows all the tea on anyone who is someone in this school, but he never engaged to show off his theatrical abilities in one of the semesterly plays the academy puts out. That is Lee Jooheon’s territory and he doesn’t want to mess with Joohoney.

“No, no,” Minhyuk chuckles, “I’m just really eager to − ” The way Hyungwon suddenly turns and gives him his full attention makes the older boy freeze, like a cat rolling on her back out of the blue and expecting to be pet while showing adorable, soulful, yet desperately bored eyes. Understandable, no one in their right mind would be excited to solve maths equations unless they are as tall as a garden dwarf. “To help y-you,” comes a stutter. Minhyuk gulps his nervousness so uncalled for and plasters back his confident grin on. Hyungwon doesn’t look too impressed though, in fact, he shows clear signs of annoyance by how he points to an exercise with the tip of his pencil. “Then explain to me, how do you solve this?”

 

「

    1)  Given the following _f_ : (0, +∞)→ **R** , _f_ (x)=   **eˣ**  +ln x +1

 **5p** a) Prove that _f ‘_ ( _x_ ) = **eˣ**  + 1/ **eˣ**   , x ∈ (0, +∞).

 **5p** b) Determine the equation of the tangent to the function f graphic in the point x0=1 on the x-axis found on the graphic.

 **5p** c) Prove that the equation _f_ ( _x_ )=0 has a unique solution in the interval (0,1).

                                                                                                                                                                                                  」

 

Minhyuk reads the sentence a few times to make sure nothing is hidden in there to give away the solution. Like, let’s say, the actual solution. He reads again, humming this time to give the impression that he’s actually considering how to solve this function and its derivative when in fact he’s absolutely just buying time. If he was doing his own homework right now, which really never happens, he’d text Kihyun a shot of the exercise, lots of pleading eyes emojis and a promise to buy him coffee before his friend would give in and help his hopeless half braincell ass. It’s the only algorithm Minhyuk knows to work. However, if he asked Kihyun for help right now when Hyungwon is watching him with scrutiny, he’s sure the popular boy would just take his things and leave (and probably ask Kihyun directly for help).  

“Well, let’s start with a) first!” he decides, full of the same enthusiasm from before, despite the cold sweat sliding down his nape. Hyungwon gives him the same impassable look though. Geez, for somebody who’s getting tutored on maths he surely judges others a lot for being bad at maths. Minhyuk scrunches his nose and tries to do it by himself, he thinks of all those classes he had last semester and how many similar exercises they’ve solved. Surely with some brainstorming, he could come up with the solution. “Shouldn’t we use the table of derivatives for that one?” Hyungwon suggests casually. Right. The table. All functions and their derivatives behave according to this golden table they’re being forced to memorize. “Yep, exactly,” Minhyuk nods satisfied, “I’m glad you already know that.”

“Hn.” Wiping out the table from his portfolio of carefully collected handouts, Hyungwon starts to write in slightly crooked calligraphy the solution, Minhyuk hovering over his shoulder to inspect what and how he’s applying. It’s easy to follow when Hyungwon traces the formulas with his index on the paper. For a guy so organized, it’s a wonder he actually needs tutoring, Minhyuk frowns. If he could focus half as well as Hyungwon − or actually, just care − he is certain he’d have no issues to pass the class and wouldn’t have to stress as much over it. Or rather, stress his friends about it. Before he realizes it, Hyungwon already wrote down the first point.

 

a) _f’_ ( _x_ ) = ( **eˣ**  +ln x +1)’= ( **eˣ**  )’ +(ln x)’ +(1)’= **eˣ**  +1/ **eˣ**  +0 =   **eˣ**  +1/ **eˣ**

 

“So productive already!” Minhyuk encourages him grinning, but really dreading how Hyungwon will probably soon enough see through his act. How in the world can he solve the rest of the exercise? What _even_ is a tangent to the graphic and how do you determine its equation? Thankfully, he could win a prize for the fastest typer in the whole academy so while Hyungwon is busy writing down the few letters and operational symbols, Minhyuk already texted Kihyun asking him about point b. And being the decent pal that he is, the nerdy sharkster replies just in time to save his face, not without inquiring about the strange mystery surrounding Lee Minhyuk’s sudden interest in Pitagora’s language of love.

 

‘ _just use the formula you idiot. y-f(x0)=f’(x0) (x-x0). replace the values and bingo. what are you doing tho?’_

 

“Alright, for the second point we need to apply the formula! Do you know it?” Hyungwon shakes his head, cheek resting lazily against the palm of his hand. “I’ve missed a few weeks from school and nobody bothered to explain to me all the stuff that’s been taught already,” the boy sighs and now Minhyuk feels sincerely bad for him. Bad for what he’s doing, taking advantage of his time in such a selfish manner when Hyungwon is simply trying to make up for the lost classes. Maybe he really is an idiot like Kihyun called him for forgetting the fuss all around school the few weeks Hyungwon’s been gone, rumors flying left and right only to be proven wrong when the boy returned with a doctor’s note for going down with the flu. “Here, let me,” he whispers gently and takes the pen and paper from Hyungwon’s long and elegant fingers. Fitting for a pianist, Minhyuk muses but says nothing as he struggles to apply what the expert geek told him to. “So…”

 

b) _y-f(x0)=f’(x0) (x-x0)_

 _y-(_ **_e¹_ ** _+ln 1 +1)= (_ **_e¹_ ** _+1/_ **_e¹_ ** _)(x-1)_

_y-(e+0+1)=(e+1/e)(x-1)_

_y-(e+1)=(e+1/e)x-(e+1/e)_

_y-e-1-(e+1/e)x+e+1/e=0_

_(e+1/e)x+y+1/e=0 is the equation of the tangent to the function f graphic in the point x0=1_

 

“That...looks a bit weird,” the older frowns and Hyungwon nods in approval from beside him. Usually, these sort of exercises had some obvious, natural-like solutions. Minhyuk’s pretty sure that _e_ buddy is not natural and has lots of additives that make him so bloated. After a moment, Hyungwon shrugs and notes down the newly given formula that should be useful in the future even if Minhyuk’s solution might be completely off. Then, as though back to square one, the two boys stare at point c not understanding one single word and becoming temporarily functional illiterates. Once more, Minhyuk takes his phone from his pocket and sends an s.o.s to Kihyun, asking him how to determine that _f_ ( _x_ )=0 has a unique solution. And if possible, a step-by-step guide would be very welcome right about now.

“Uh, we should start with…” he mumbles, hoping for another cell than the lonely one swimming around his brain to ring and come up with something useful. Kihyun doesn’t disappoint − he never does, bless him − and starts live-texting the whole solution, a complete _a la carte_ textbook solution. Minhyuk could kiss him for this. “Holy shit,” Minhyuk gasps not believing his luck. When he turns his attention back to his tutoring date though, Hyungwon watches him, dare he say, slightly amused and with a raised eyebrow. “Right, so first we calculate the...lim..oh, the limits! of the function.” The amused look seems to intensify while an embarrassed burning blush blooms on Minhyuk’s cheeks, a fear of being caught cheating creeping up on him and making him fidget in his seat.

“Aha,” Hyungwon eggs him on, back to leaning with his cheek in his palm. What a tease, Minhyuk feels totally infuriated. And maybe a bit enamored as well. “O-one limit should be less than 0 and the other more than 0 and since the function is...cont..continental?” Being discreet about cheating is not that easy when you have no idea what exactly you’re supposed to write, Minhyuk discovers. To his horror, Hyungwon corrects him, “You mean continuous?” The same teasing tone from before gets Minhyuk to shove his phone back in his pocket and stare down at his hands, his face too red to recognize the school’s joker. From kissing Kihyun, his plans might need to change to another k-word that is even more frowned upon. He’s sure jail is not that bad though. “Yeah, continuous,” the boy replies dryly, “and that results in a unique solution.”

“Huh,” is all that Hyungwon says. The audacity! Pushing Minhyuk into making a fool of himself and then not even having the decency to pretend that he’s at least feeling bad about it. Chae Hyungwon is truly a rotten man, Minhyuk pouts with his arms crossed. A stunning yet rotten man. He expects the popular boy to mess around some more now that he clearly figured out Minhyuk’s knowledge in maths is as extensive as a finite assemblage, but he doesn’t. Instead, the rotten Chae Hyungwon follows his instructions carefully, calculates the limit in 0 and then in 1 and sure enough, they come out like Minhyuk said they would. There are a few lines missing to make it a complete solution and they have no idea what theorem they used to prove what had to be proven, but they did it. They solved all three points in a little less than half an hour. “Why did you sign up for this if you’re worse than me?”

Minhyuk winches at the harsh wording and wants to retort that, hey, last time he checked he actually passed math, unlike his peer who even had to sign up for tutoring. But he doesn’t. The boy only fidgets some more, idly playing with his own fingers and avoiding Hyungwon’s gaze, too embarrassed to admit he pulled this stunt all for a silly crush. Hyungwon’s smile though melts slightly, the irregular shape of his lips emphasized even more when he reaches out and takes Minhyuk’s hand in his own, disrupting the boy’s positively entertaining inner monologue. “How about next time, your friend texting you the answers will tutor us both?” Minhyuk opens his mouth to object, definitely not up to hang out with both Kihyun and Hyungwon in a damn library and do maths. He can’t imagine any worse way to spend his day.

“And then I can take you out on a coffee date,” comes the final punch line that literally punches the air out of Minhyuk. A date? With _the_ Chae Hyungwon? He doesn’t need a probability formula to know he’s not going to miss that chance. The solar energy returns full force into his body and he nods one too many times to the offer before getting up, his chair screeching quite loudly against the old floorboards. The librarian already knows where to send a nasty glare but Minhyuk couldn’t care less. He’s got a date with Chae Hyungwon. “Let’s work from the bottom of the equation this time and start with the coffee instead,” the boy extends his hand to Hyungwon who gladly takes it. Homework would have to be left dead in a ditch for another day.

**Author's Note:**

> my dms are always open on twitter @seoulfulnights


End file.
